Analysis of hydrodynamic patterns in the coastal waters of the Caspian Sea using field measurements

Extended Abstract

The Caspian Sea, the largest enclosed inland body of water on Earth, is bordered by five countries: Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. It has a unique geographical setting with a surface area of approximately 371,000 square kilometers and a maximum depth of about 1,025 meters. The climate around the Caspian Sea varies significantly, with the northern part experiencing cold winters and hot summers, while the southern part has milder winters and hotter summers. The general wind patterns and atmospheric systems affecting the Caspian Sea include the Siberian High, which brings cold air masses, and the Azores High, which influences the summer weather. The overall water circulation in the Caspian Sea is cyclonic, and wave conditions are influenced by wind patterns and the basin's morphology.

The southern coast of the Caspian Sea is characterized by diverse bathymetric features, with depths ranging from shallow coastal areas to deeper offshore regions. The coastal morphology is influenced by sediment deposition and erosion processes, which are driven by wave and current dynamics. The general circulation of water in the southern Caspian Sea is influenced by wind-driven currents and the basin's topography, leading to complex flow patterns. Wave conditions in this region are primarily affected by local wind patterns and can vary significantly depending on seasonal changes.

Field measurements of wave and current parameters are crucial in oceanographic studies as they provide essential data for understanding the physical dynamics of marine environments. These measurements help assess the impact of climatic changes on ocean circulation, wave patterns, and coastal erosion. Accurate field data are necessary for validating numerical models and improving the predictability of oceanographic phenomena, which is vital for coastal management and marine resource exploitation. Despite its significance, the Caspian Sea lacks comprehensive oceanographic data, particularly regarding wave and current measurements. This scarcity of data hampers the ability to fully understand the sea's dynamic processes and their implications for the surrounding environment. The limited availability of observational data is a significant challenge for researchers, making it difficult to develop accurate models and forecasts for the region.

Recent studies have utilized Acoustic Doppler Current Profilers (ADCP) to measure wave and current parameters in the Caspian Sea. In 2010, Ghaffari and Chegini conducted a study titled "Acoustic Doppler Current Profiler Observations in the Southern Caspian Sea: Shelf Currents and Flow Field off Feridoonkenar Bay, Iran." This research involved offshore bottom-mounted ADCP measurements and wind records to characterize current fields in the continental shelf and offshore deeper regions in the southern Caspian Sea. The results indicated that long-period waves dominate the current field in the continental shelf off Feridoonkenar Bay. The study found that the prevailing wind patterns significantly influence the current profiles observed during the measurements. In 2014, Firoozfar and Neshaei researched sediment deposition and erosion processes along the southern coast, showing that local wave patterns significantly impact coastal morphology. In 2024, Zavialov and Kostianoy conducted a study on the Kazakhstan shelf of the Caspian Sea, revealing that the currents were predominantly along the shore but simultaneously variable in direction. The results also indicated that the along-shore wind stress significantly influenced the wave and current dynamics. In 2019, Masoud et al. conducted a study titled "Low-Frequency Variations in Currents on the Southern Continental Shelf of the Caspian Sea." This research evaluated wind-induced currents along the southern Caspian Sea, revealing that low-frequency variations in currents were significantly influenced by wind patterns.

In this study, considering the importance of field measurements in oceanography and the lack of this type of information in the Caspian Sea, wave and current information was recorded at seven nearshore stations (five 10-meter stations and two 30-meter stations) on the southern coast of the Caspian Sea in Iran over more than a year. This information was recorded in different water column layers, which in this study considered surface and bottom layer information. Then, the recorded information was analyzed and examined temporarily and spatially. For this purpose, various diagrams were used, including wind rose, wave rose, scatter diagram, and radar diagram.

The results confirmed the counterclockwise circulation of the Caspian Sea's currents. On the southern coasts, the predominant current direction aligns with this general circulation, except at the Roudsar stations, where local eddies reverse the flow. Although the overall pattern was consistent, significant spatial and seasonal variability was observed. At Amirabad and Anzali, reversing currents differed due to wind-driven water level fluctuations and coastal morphology. Among all stations, Anzali exhibited the highest energy levels regarding wave and current activity. Additionally, seasonal variations were observed, with winter recording the most intense currents and highest waves at most stations.

Wave direction also varied by location and season. At western stations, the most frequent and substantial waves originated from the north and northeast, while at eastern stations, they came from the north and northwest. The central station at Noshahr predominantly recorded waves from the north. These patterns were influenced by regional wind systems, including the Siberian High and Azores High, which affect seasonal weather and wave formation.

Although the counterclockwise circulation was dominant, the presence of reversing currents at specific stations—particularly Roudsar—highlighted the complexity of local hydrodynamic processes. These reverse flows, shaped by topographic features and localized eddies, underscore the need for site-specific analysis in coastal modeling. The observed differences between surface and bottom currents, as well as the stratification of energy levels, further emphasize the importance of vertical profiling in understanding marine dynamics.